The present invention relates to a variable pulse-length modulator, in particular for radar transmitters, and to a radar incorporating such a modulator.
The modulators currently used in radars which employ pulsed emission may be divided into three main categories.
Modulators which are known as vacuum tube modulators employ a triode, or tetrode tube as their switching means. Such modulators allow pulses of continuously variable length to be generated, or a large number of pulses of differing duration. The low internal impedance of such devices enables them to be matched to loads of various kinds. However, such modulators have the drawbacks of high weigth and volume and poor reliability. In addition, the presence of a storage capacitor and the high voltage level employed in devices of this kind make it necessary to provide careful safeguards both for the equipment and the personnel using it.
Delay line modulators, because of the lower voltages employed, are of more reasonable dimensions, weight, volume and cost.
However, the capacity which such modulators have for adaptation to situations where varying pulse lengths and/or operating impedances are required is much more limited. What is more, whith a delay line of acceptable size the shape of the pulses is much less satisfactory than from a vacuum-tube modulator.
Magnetic modulators in which energy is stored in an inductance carrying a large DC current and is then released by interrupting this current, have the disadvantages that the pulse produced is unstable with time and that their efficiency is poor because of the conditions under which the inductance is charged.